I don't think you've used .NET Core recently if you're saying that it feels half-finished. This is just FUD. At this point, .NET Core, especially 2.0, is excellent for almost every use case except native app development. Even then, you've got .NET Native attempting to solve that problem. The last time .NET Core was "half-finished" was probably its 1.0 release.

For its intended purpose, it is ready enough and stable. But that is the point of open source as well, to have outside input into decisions made early on. Besides, is anything release actually fully ready yet? I don't think releasing it was a bad idea. .Net Core does seem to be moving fast but things are now stabilizing and it has been a combined effort of internal and external Microsoft developers, which is great for them. If they had simply released another .Net framework 5, I think a lot of developer mind share would have gone elsewhere. Open source was the right decision, and despite it feeling half-finished, it's actually a great improvement. Things will stabilize.

It is an open source project, if they don't release it they cannot start receiving community feedback, patch sets, and bugs. Which means a lot of stuff still won't be found until it is released, no matter when that is.

.Net Core is definitely half baked but it is a pretty ambitious undertaking. They're completely re-developing .Net from the ground up to be cross platform, no small task.

They recommend not using Kestrel for an internet facing app and I agree. There is no reason not to use it for services that are not internet facing.